SBGH10 (JED version) questions

[jdkent]

Hello,
I have just built a SBGH (JED), but haven't put any reflector on it as yet (I have posted my preliminary results in the Oakville/Mississauga thread). This is my next step.
I have followed JED's plans for the elements and am wondering about what type of reflector would be the best. Answers to the following questions would be greatly appreciated:

1) In JED's plans (G10), it shows a gap (G1, G2, G3, G4, G5) between the co-linear rods - how important are these gaps? ie, can a straight rod be used instead of 2 rods spaced with a gap? And if so, will there be much difference in the how the reflector works?

2) Would a sheet of aluminum foil over cardboard work as well? Weather durability isn't too much of an issue right now as this will be going in my attic.

Which of the above options would give me the strongest signal?

Thank you so much in advance for any anwers!

Cheers,
Jeff

[300ohm]

1) In JED's plans (G10), it shows a gap (G1, G2, G3, G4, G5) between the co-linear rods - how important are these gaps? ie, can a straight rod be used instead of 2 rods spaced with a gap? And if so, will there be much difference in the how the reflector works?

The gaps are very important gain and tuning items for the colinear rod models. Any deviation from the model means the antenna wont follow the model. Without the gaps, youll lose a good db in gain and the gain pattern will be different too.

2) Would a sheet of aluminum foil over cardboard work as well? Weather durability isn't too much of an issue right now as this will be going in my attic.

Xauto mimicked the gaps in aluminum foil over cardboard with one of his reflectors, and it worked pretty well. Again, since it deviates from the model, it wont follow the models graphed patterns.

[j3d]

Originally Posted by jdkent

1) In JED's plans (G10), it shows a gap (G1, G2,
G3, G4, G5) between the co-linear rods - how important are these gaps?
ie, can a straight rod be used instead of 2 rods spaced with a gap?
And if so, will there be much difference in the how the reflector
works?

The gaps are very important. Deviating from the model will reduce
bandwidth and increase the SWR. Sometime I may create a model that
has no gaps but I can say now that it will not perform as well.

2) Would a sheet of aluminum foil over cardboard work as well?
Weather durability isn't too much of an issue right now as this will
be going in my attic.

Again, the answer is the same. The zigzags were optimized for the 10
co-linear rods.

Also keep in mind that the antennas were designed in free-space and
that the antenna will likely have different properties in the attic.
Also try to minimize the length of coax between the antenna and your
TV.

Here is a simple idea for the reflecting rods that you might want to
pursue: Create a co-linear rod using aluminum tape and a wooden dowel
of the appropriate diameter. Simply encircle portions of the dowel
that correspond to the rod with the aluminum tape. I have no idea how
well this will work but it seems like an inexpensive option.

Good luck,
--John

[300ohm]

Simply encircle portions of the dowel
that correspond to the rod with the aluminum tape.

Great idea for attic use. I would do a neat job with aluminum foil wrapped around the dowel and scotch tape to hold. Some of the "aluminum" duct tapes Ive metered have varying degrees degrees of conductivity. I found the stuff I have isnt good enough to do a cpu pin mod.

Hot dipped galvanized dowel anyone ?, heh.

[Feig]

Hi I'm using 9 ga glavinized steel wire which can be soldered. I would like to know on the JED sbgh10 rev2 what would be the distance if I solder a wire to the feed gap taking it towards the centre and bending it 90 degrees back behind the reflectors where I want to attach the balun.

Feig

[300ohm]

I would like to know on the JED sbgh10 rev2 what would be the distance if I solder a wire to the feed gap taking it towards the centre and bending it 90 degrees back behind the reflectors where I want to attach the balun.

Why do you want to do that ? Baluns are that heavy.

The distance would be the reflector to element distance of 100 mm plus how far behind the reflector you want to go.

[Feig]

I can feed the wire through a cpvc cross piece eliminating the need to support the feed point. The wire would be long enough (100mm+ past bend)) so that the balun is attached on the rear of the reflector. I seen something that for twin wire leads the distance between the wires must be at least 6 times the diameter. The wire I am using is 4mm. I was wondering if the best distance would be similar to the phase lines on a dbgh or take the wire straight back from the feed point.

I would attach the balun 20mm behind the reflector.

Feig

[Xauto]

If you are looking for impedance of parallel wire Z=276log2S/d S= center to center space and d= diameter of conductor. If you are looking for 300 ohm and d=4mm S is about 25mm.

[Feig]

Thank You

Feig

[j3d]

Originally Posted by Feig

Hi I'm using 9 ga glavinized steel wire which can
be soldered. I would like to know on the JED sbgh10 rev2 what would
be the distance if I solder a wire to the feed gap taking it towards
the centre and bending it 90 degrees back behind the reflectors where
I want to attach the balun.
Feig

I would avoid doing that because you would probably end up changing
the feed point impedence causing a net-gain loss and a reduction in
bandwidth.

--John

[300ohm]

Why do you want to do that ? Baluns are that heavy.

Heh, typo, baluns are not that heavy.

All baluns can fit inside of 3/4 inch pvc pipe. A lot can fit inside of 1/2 inch pvc pipe.

[Feig]

I would of thought that a neat soldering job with nice clean lines would be better than a nut and bolt and not effect the impedemce as much.

Feig